Photoelectric scanning device for flame cutting machines

ABSTRACT

A photoelectric scanning device for flame cutting machines includes a disc rotor motor as the driving motor for the scanning shaft and a disc rotor motor as the generator for producing the damping voltage.

United States Patent [191 Hahn et a1.

[11] 3,812,412 1 May 21, 1974 1 1 PHOTOELECTRIC SCANNING DEVICE FOR FLAME CUTTING MACHINES [75] Inventors: Gunter Hahn, Hausen; Gunther Hannappel, Frankfurt, both of Germany [73] Assignee: Messer Griesheim GmbII, Frankfurt/Main, Germany [22] Filed: Nov. 9, 1971 [21] Appl. No.: 196,907

Related U.S. Application Data [63] Continuation-impart of Ser. No. 801,506, Feb. 24,

1969. abandoned.

[52] U.S. Cl 318/577, 318/576, 310/268 [51] Int. Cl. G051) 19/36 [58] Field of Search 318/576, 577; 310/268 [56] References Cited UNITED STATES PATENTS 2,522,851 9/1950 Tyrner 318/577 3,231,807 l/l966 Willis 310/268 X 2,499,178 2/1950 Berry et al. 318/577 3,496,437 2/1970 Layden 318/577 Primary Examiner-T. E. Lynch Attorney, Agent, or FirmConnolly and Hutz 5 7 ABSTRACT A photoelectric scanning device for flame cutting machines includes a disc rotor motor as the driving motor for the scanning shaft and a disc rotor motor as the generator for producing the damping voltage.

3 Claims, 5 Drawing Figures lac-Motor ToMotorZ PHOTOELECTRIC SCANNING DEVICE FOR FLAME CUTTING MACHINES CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 80l,506, filed Feb. 24, 1969 now abandoned.

BACKGROUND OF INVENTION This invention relates to a photoelectric scanning device for flame cutting machines, wherein the movement of the scanning shaft is caused by a driving motor and which furthermore is provided with a generator for producing the damping voltage and a resolver for the control of the coordinate drive depending on the setting.

Various processes are known which scan lines and patterns by means of light-sensitive switching elements, short light receivers. In many devices the most contrasting line or pattern edge is projected by way of an optical system on the light receiver. In a known device for the scanning of lines, the light receiver consists of two light-sensitive, variable resistors, each of which forms a branch of an electrical bridge. They are equalized when both resistors are of the same value, i.e. if the resistors are illuminated in the same manner. In this instance, the line to be scanned is located exactly in the axial direction of the light-sensitive resistors. In order to maintain this state, the resistor combination is mechanically coupled with a motor whose error signal is conducted from the diagonal voltage of the bridge. In order to prevent an over-swinging of the motor, a damping is indispensable. The voltage required for this damping is produced by a tach generator of common construction generally directly coupled with the motor axis. According to the type of bridge supply voltage, an alternating current motor, preferably a Ferraris motor, or a direct current shunt-wound electric motor is used. The deciding characteristics of these motors should be high initial torque and high acceleration. The first is required in order to quickly overcome equilibrium friction and mass moment of inertia of the shaft supporting the light receiver and of the gear parts situated between this shaft and the motor in tach generator. A high acceleration is necessary in order to be able to scan satisfactorily rectangular curves or pointed angles with the smallest roundness radius and a fast advance speed.

The typical starting times of customary scanning motors including tach generators for photoelectric scanning devices are between about 50 and 120 ms. The starting of the scanning shaft supporting the light receiver in the known embodiments, however, is approximately twice as long as a result of mass moment of inertia of the gearing between motor and scanning shaft required for torque increase, the reduction of speed ratio amounting to about 20:1. W it h such a device, radii of g 35 mm can be circumscribed at a scanning speed of 6 m/min, which is reached in plasmic cutting, for example. A minimum radius of such size often becomes undesirable at the above-mentioned speed because of constructive and economic reasons. Furthermore, it is desirable to have scanning true to the original pattern even at high speeds.

SUMMARY OF INVENTION The object of this invention is to provide a drive for the photoelectric scanning devices for flame cutting machines, known per se, which are provided with a driving motor for the scanning shaft and a generator for producing the damping voltage, the drive allowing to circumscribe very samll radii even at high cutting speeds.

According to the invention, the above object is achieved in that for each of the driving motor and the generator a disc rotor motor is employed. In an advantageous further development of the invention, furthermore, the gearing required between driving motor and scanning shaft is replaced by a geared belt.

The advantage of the invention consists in that the starting times of driving motor and generator are considerably shortened, since disc rotor motors have an extremely low mechanical time constants. Furthermore, the reduction of speed ratio between driving motor and scanning shaft in using disc rotors motors can be reduced to less than 10:1. The idle bulk of the gearing to be moved is thereby decreased and the starting times further lessened.

In an advantageous embodiment of the invention, the gearing is replaced by a geared band. This embodiment is particularly advantageous in using a resolver for the position-dependent control of the coordinate drive of the cutting machine, since the coordination of the rotation by driving shaft, scanning shaft and resolver shaft can be carried out very exactly with the help of a geared band.

THE DRAWINGS FIG. 1 is a perspective view schematically illustrating the inventive scanning device in a torch cutting machine assembly;

FIG. 2 is a cross-sectional view in elevation of a scanning device or photoscope in accordance with this invention;

FIGS. 3-4 are cross-sectional views taken through FIG. 2 along the lines 3-3 and 4-4, respectively; and

FIG. 5 is a view similar to FIG. 30f a modification of this invention.

DETAILED DESCRIPTION This invention makes use of arrangements known in the art as disc rotor motors, disc dynamo electric machines, or printed circuit motors. Such disc rotor motors heretofore were developed especially for use in very small space between structural elements (for example for moving window panes in automobiles and for activating windshield wipers, etc.). In the case of a photoelectric scanner device, such small spaces necessitated by consideration of design do not exist, so that the dimensions of the motors used do not depend on the configuration of the other structural elements such as is, for example, the case with, windshield wipers. Thus it was for this reason alone not obvious that a disc rotor motor could be used in a photoelectric scanner as drive motor and as generator.

In the known photoelectric scanners, normal alternating current motors were used prior to this invention. Their operating voltage is about 60 V (cf. US. Pat. No. 3,135,904). These alternating current motors were employed as drive motors and as generators. As previously pointed out a damping device must necessarily be provided in order to prevent overshoot of the drive motor. The voltage required for damping is generally produced by an AC tachogenerator directly coupled with the motor axle. This generator produces an alternatingcurrcnt voltage which is transformed into a direct cur rent only by certain filter sections, for example condensers or rectifier bridges. Because of these filter sections which all have a time constant exceeding ms, damping in case of a change of speed of the drive motor occurs with a certain delay. This exerts an unfavorable influence on the control accuracy of the drive motors.

Therefore it was the goal of the invention to design a drive for a photoelectric scanning device equipped with a drive motor for the scanner and a generator that produces the damping voltage. This drive had to produce damping without delay and had to have a very brief starting time of the motor or generator, respectively, so that very small radii could be circumscribed at high cutting speeds. In order to solve this problem one adjustable disc rotor is used for the drive motor and another one for the generator.

This eliminates the above filter sections required by the prior art. It is further possible that even at very high cutting speeds up to 6 m/min. and with very abrupt changes of the line to be scanned (for example a 90 turn when the radius is very small), damping of the motor that begins immediately can be achieved so that overshoot of the latter is avoided.

One of the extreme requirements concerning follower control devices is that the motors for the photoelectric scanner must have a wide regulator ratio. Regulator ratio in this context means the ratio of the fastest and the slowest number of rotations of the motor. This regulator ratio is obtained for the alternating-current motor and for the disc rotor motor through changing the operational voltage of the motors, i.e. if a motor runs at 80 V operational voltage at the highest number of rotations, the operational voltage must be changed at the same ratio as the desired number of rotations. Assuming that the number of rotations is to be reduced at the ratio of l:l000, the operational voltage in this instance amounts to only 0.08V. Regarding the alternating-current motors used so far, this ratio of changing the number of rotations was the maximum possible ratio. If, on the other hand, disc rotor motors are used, the operation voltage ranges from 6 to 24 Volt. Thus despite an operating voltage that is ten times smaller, a regulation ratio that is three times greater, i.e. lz3000, can be achieved with this invention.

In FIG. 1 a torch cutting machine 10 is illustrated. The torch cutting machine has a longitudinal carriage 11 with a jib 11'. The longitudinal carriage 11 is movably arranged on two longitudinal tracks 12, 13.

Between the longitudinal tracks l2, 13 there is arranged on a platform 14 the sheet of metal 15 and on a movable pattern platform 16, arranged beneath the jib 11 there is arranged the pattern original to be scanned. A cross-carriage is provided at the longitudinal carriage 11, the former having a drive 18 for the cross-movement of the carriage l7 and of a novel photoscope 19 mounted at carriage 17, as well as of the four torch carriages 20-23 provided movably at the longitudinal carraige 11. The torch carriages 20-23 are firmly connected by means of a connecting rod 24 with the photoscope 19. At each of the torch carriages 20-23 there is arranged a cutting torch 25 as well as a capacitative scanning arrangement 26, known per se, with a scanner 27, serving as an actual value indictor, for the torch elevation adjustment.

During operation of the torch cutting machine 10, the photoscope l9 follows at a certain speed the line of a drawing, which lies on table 16. Within the photoscope 19 movement directions are given (as later described) by means of electrical units to the driving motors l8 (transverse movement) and 28 (longitudinal movement).

The construction of photoscope 19 as well as the arrangement of the units provided in the photoscope are shown in FIG. 2. Photoscope 19 has a scanning head 29, a resolver 30, a motor 31, a generator 32, as well as an amplifier 33. Scanning head 29, resolver 30 and motor 31 are connected by means of gears 34, 35 and 36 as well as toothed belt 37.

According to the invention, motor 31 as well as generator 32 are constructed as disc rotors. The disc rotor motor 31 consists of a housing wherein by means of a drive shaft 39, the rotor (shaped as a disc 38) of the motor is turnably supported. Furthermore, permanent magnets 40 are arranged in the housing. Disc 38 has a plurality (170, for example) of windings 41 (see FIG. 4) to which current is supplied by means of carbon brushes designated by 42. I

windings 41 in a disc rotor motor are not formed by the winding of a wire (for example a copper wire). Moreover, disc 38 consists of a plate provided with a current conducting coating. Windings 41 result by the etching away (as in the preparation of printed circuits) or by the punching out of the areas of the metallic coating designated in FIG. 4 with A (front part) or B (back part).

Disc 38 is firmly connected by means of shaft 39 with disc 43 of the disc rotor generator 32. The generator 32 equally has permanent magnets and carbon brushes which are designated with 44 or 45.

The manner of operation of the device is as follows:

one or on the other photoelectric cell 48, 49, a signal is produced which is conducted to an operation amplifier 50. The starting signal is conducted to a theoretical/actual value-reference input element 51, whose starting signal is conducted to the disc motor 31 upon being amplified by means of three operation amplifiers which is conducted by way of leads 55 to the theoretical/actual value reference input element 51.

On the otherhand, there result, as known, various starting signals X and. Y in the turning of the resolver, the signals being conducted to motors 18 or 28 of the torch cutting machine illustrated in FIG. 1.

As indicated by P16. 2, between the operation amplifier 52 and the operation amplifier 53, there is provided a voltage divider 56 by means of which the current conducted to motor 31 may be adjusted. To the voltage divider 56 there is connected at the outlet side a reference input element 57 in that the starting signal of the voltage divider 56 (actual value) is compared with the starting signal of the operation amplifier 54. Due to this circuit twice the theoretical/actual value comparison an optimum control of the movement of the scanning head is achieved.

This invention is not limited to the specific embodiments shown herein. For example although FlG. 3 illustrates the optical shaft gear 35 to be between drive gear 34 and resolver gear 36, other arrangements are possible. Thus FIG. 5 illustrates the gear 36 of resolver to be between'gear 34' for shaft 39' of motor 31' and gear 35 of scanner 29' with belt 37 transmitting the drive motion.

As shown by FIG. 2, the operation amplifiers 50, 52, 53 and 54 are illustrated only symbolically, since these customary units are sold, for example, by Motorola Company Motorola Semiconductor Products under the desingation MC 14390. By the use of the disc rotor as the motor and generator in combination with the above-described amplifier design, it is advantageously achieved that immediately after the change in the course of the curve of the drawing line 58 and the resulting change in the amount of light falling on the photoconductive cells 48, 49, there already results a starting signal at the operation amplifier 54, the signal is conducted to the re-turning disc rotor motor 31 and on the basis of the high starting moment of rotation in combination with the high acceleration of the motor, the scanning head 29 as well as resolver 30 are immediately rotated. By this direct actuating, when the actuating time is reduced by more than one-half as compared to the known scanning devices (actuating time now 40 ms. previously 100-240 ms.), it becomes possible to use photoconductive cells 48, 49 having small dimensions.

It has become possible to use photoconductive cells with a scanning surface of 0.6 mm square. This small scanning surface is also sufficient, in a sudden break of the line 58 to be scanned, to give off a signal which on the basis of the amplifier and disc rotor motor/disc rotor generator unit, provided by the invention, then leads directly to an adjustment of the scanning head into the new scanning direction before the effective scanning surface of the photoconductive cells is moved beyond the bending point.

In the previously published scanning devices, it was necessary to make the effective scanning surface of the photoconductive cells larger, specifically 2.0 X 0.8 mm, in order to avoid this running out. Because of this relatively large dimensioning of the photoconductive cells, however, a certain minimum distance away from two side-by-side lines on a drawing is required. Because of the small dimensioning of the photoconductive cells made possible by the invention, it is furthermore achieved that this distance may be made shorter than 1 mm. This is advantageous especially in view of the utilization of the sheet of metal to be cut, since the individual parts are stacked more closely and thus the waste is reduced to a minimum.

What is claimed is:

1. In a torch cutting machine having cutting means and motor means for causing the movement of the cutting means and a photoelectric scanning device, the improvement comprising said photoelectric scanning device including a scanning shaft, an optical system at one end of said scanning shaft, light receivers in said scanning shaft remote from said optical system, light source means for said optical system, a disc rotor drive motor, a disc rotor generator, a drive shaft, said disc rotor drive motor and said disc rotor generator being coaxially mounted on said drive shaft displaced from said op tical system and said light source means and out of the path of light from said light source means, a resolver, means connecting said resolver to said motor means whereby said motor means causes the movement of said cutting means in respons to said resolver, said resolver being displaced from said drive shaft and said scanning shaft, circuit means interconnecting said generator and said light receivers for causing said generator to respond to said light receivers, and common gear means interconnecting said scanning shaft and said drive shaft and said resolver whereby said disc rotor drive motor is actuated in accordance with the light sensed by said optical system when said optical system scans a pattern to thereby cause said cutting means to follow the pattern scanned by said optical system.

2. A device as set forth in claim 1 wherein said circuit means includes amplifier means connected between said light receivers and said disc rotor drive motor and disc rotor generator.

3. A device as set forth in claim 1 wherein said common gear means includes a driving pinion mounted on said drive shaft, a sprocket wheel mounted on said scanning shaft, a driven gear connected to said resolver, and a geared band mounted around said driving pinion and said sprocket wheel and said driven gear. 

1. In a torch cutting machine having cutting means and motor means for causing the movement of the cutting means and a photoelectric scanning device, the improvement comprising said photoelectric scanning device including a scanning shaft, an optical system at one end of said scanning shaft, light receivers in said scanning shaft remote from said optical system, light source means for said optical system, a disc rotor drive motor, a disc rotor generator, a drive shaft, said disc rotor drive motor and said disc rotor generator being coaxially mounted on said drive shaft displaced from said optical system and said light source means and out of the path of light from said light source means, a resolver, means connecting said resolver to said motor means whereby said motor means causes the movement of said cutting means in respons to said resolver, said resolver being displaced from said drive shaft and said scanning shaft, circuit means interconnecting said generator and said light receivers for causing said generator to respond to said light receivers, and common gear means interconnecting said scanning shaft and said drive shaft and said resolver whereby said disc rotor drive motor is actuated in accordance with the light sensed by said optical system when said optical system scans a pattern to thereby cause said cutting means to follow the pattern scanned by said optical system.
 2. A device as set forth in claim 1 wherein said circuit means includes amplifier means connected between said light receivers and said disc rotor drive motor and disc rotor generator.
 3. A device as set forth in claim 1 wherein said common gear means includes a driving pinion mounted on said drive shaft, a sprocket wheel mounted on said scanning shaft, a driven gear connected to said resolver, and a geared band mounted around said driving pinion and said sprocket wheel and said driven gear. 